A detachable fastener is known from U.S. Pat. No. 3,263,727. A first embodiment of the known fastener includes three elements, namely a screw and two spring washers being associated with the screw. In another embodiment of the known fastener, one of the spring washers is integrated into the screw. The other spring washer forms some sort of a securing element. The screw includes an engagement surface for a wrench, a threaded portion and a supporting surface to transmit an axial force onto the securing element. The securing element includes a counter supporting surface and a contact surface to transmit the axial force onto a component. The screw at its supporting surface facing the securing element includes a first wedge-shaped surface tooth arrangement, and the securing element at its counter supporting surface facing the screw includes a corresponding second wedge-shaped tooth arrangement. The wedge-shaped surface tooth arrangements form sliding surfaces sliding upon one another under an increase of the axial force in the fastener when rotating the screw with respect to the securing element in the loosening direction of rotation. In this way, a securing effect is attained. The angle of inclination of the sliding surfaces is greater than the angle of inclination of the thread of the threaded portion of the screw. The sliding surfaces being active in the loosening direction of rotation are interconnected by shoulders. These shoulders extend in the direction of the axes, and they serve to attain positive engagement in the tightening direction of rotation. The shoulders are designed such that the securing ring is commonly rotated with the screw when introducing torque into the screw in the tightening direction of rotation. When loosening or untightening the screw, the sliding surfaces of the wedge-shaped surface tooth arrangements skip and they move beyond one another, respectively, preferably without exceeding the yielding point of the material. Due to this skipping effect, there is substantial wear and tear at the wedge-shaped surface tooth arrangements such that it is not possible to reuse the known fastener.
Another detachable fastener for a wheel of a motor vehicle, meaning a wheel screw, is known from German Patent Application No. 100 34 748 A1 corresponding to U.S. Patent Application Ser. No. 2002/0015628 A1. The known wheel screw includes a screw element and a supporting ring which together form the fastener. The screw element includes an engagement surface for a wrench, a threaded portion and a supporting surface to transmit an axial force onto the securing element. The securing element includes a counter supporting surface and a contact surface to transmit the axial force onto a component. The screw at its supporting surface facing the securing element includes a first wedge-shaped surface tooth arrangement, and the securing element at its counter supporting surface facing the screw includes a corresponding second wedge-shaped tooth arrangement. The wedge-shaped surface tooth arrangements form sliding surfaces sliding upon one another under an increase of the axial force in the fastener when rotating the screw with respect to the securing element in the loosening direction of rotation. In this way, a securing effect is attained. The angle of inclination of the sliding surfaces is greater than the angle of inclination of the thread of the threaded portion of the screw. The sliding surfaces being active in the loosening direction of rotation are interconnected by shoulders. These shoulders extend in the direction of the axes, and they serve to attain positive engagement in the tightening direction of rotation. The shoulders are designed such that the securing ring is commonly rotated with the screw when introducing torque into the screw in the tightening direction of rotation. When loosening the screw element, there is the danger of the sliding surfaces of the wedge-shaped surface tooth arrangements skipping and moving beyond one another. This may result in plastic deformation and wear.
Another detachable fastener is known from PCT Application No. PCT/US92/00892 published as WO 92/14939 and corresponding to U.S. Pat. No. 5,190,423. The known fastener includes two components, namely a screw element and a securing ring. The screw element is designed as a nut, i.e. it does not include a shank. The screw element includes a first surface of engagement for a wrench, a threaded portion and a supporting surface to transmit an axial force onto the securing ring. The securing ring includes a second engagement surface for a wrench, a counter supporting surface and a contact surface to transmit the axial force onto the component. The screw element at its supporting surface facing the securing element includes a first wedge-shaped surface tooth arrangement, and the securing element at its counter supporting surface facing the screw includes a corresponding second wedge-shaped tooth arrangement. The wedge-shaped surface tooth arrangements form sliding surfaces sliding upon one another under an increase of the axial force in the fastener when rotating the screw with respect to the securing element in the loosening direction of rotation. In this way, a securing effect is attained. The angle of inclination of the sliding surfaces is greater than the angle of inclination of the thread of the threaded portion of the screw. The sliding surfaces being active in the loosening direction of rotation are interconnected by shoulders. These shoulders extend in the direction of the axes, and they serve to attain positive engagement in the tightening direction of rotation. The shoulders are designed such that the securing ring is commonly rotated with the screw when introducing torque into the screw in the tightening direction of rotation. Desired untightening of the known fastener is achieved by simultaneous uniform torque engagement at the two engagement surfaces for a wrench at the screw element and at the securing ring. This movement is somewhat difficult, and it does not necessarily result from the arrangement of the two engagement surfaces for a wrench. Usually, the two engagement surfaces for a wrench are not aligned before starting the untightening movement such that it is possible that the known fastener is not correctly loosened. In the case of starting an untightening movement only by applying torque to the screw element, the axial force in the screw element and in the securing ring will be increased when continuing the sliding movement or initiating the sliding movement for the first time such that the loosening process is aggravated. Consequently, skipping of the two wedge-shaped surface tooth arrangements cannot be prevented. Thus, wear and tear will occur at the wedge-shaped surface tooth arrangements, wear and tear having a negative influence on the possibility of reusing the fastener.
Usually, the two engagement surfaces to be engaged by a wrench will not be aligned when tightening the known fastener. Incorrect use of the known fastener may especially not be precluded when using common wrenches including a double division of the wrench surfaces for simplifying handling of the wrench. It is an advantage of these tools that half the angle of rotation compared to a conventional wrench is required to align the wrench on the surface of engagement of the screw. When using such a wrench with the known fastener, it is possible that the screw element and the supporting ring are being tightened in the wrong rotational relationship with respect to one another. The fastener will then automatically rotate back to reach the starting position being defined by the stop surfaces under operational loads. In this case, there will be undesired losses of pre-tension. Furthermore, only half the sliding path may be practically used compared to an orderly tightened joint including two correctly aligned engagement surfaces.